Biology subjects

Fransen, J.

Publications and source records attributed to Fransen, J..

4 recordsLinked to original sources

bioRxiv2021

Functional basis for calmodulation of the TRPV5 calcium channel

Within the transient receptor potential (TRP) superfamily of ion channels, TRPV5 is a highly Ca2+-selective channel important for active reabsorption of Ca2+ in the kidney. Its channel activity is controlled by a negative feedback mechanism involving calmodulin (CaM) binding. Combining advanced microscopy techniques and biochemical assays, this study characterized the dynamic bilobal CaM regulation and binding stoichiometry. We demonstrate for the first time that functional (full-length) TRPV5 interacts with CaM in the absence of Ca2+, and this interaction is intensified at increasing Ca2+ concentrations sensed by the CaM C-lobe that achieves channel pore blocking. Channel inactivation occurs without CaM N-lobe calcification. Moreover, we reveal a 1:2 stoichiometry of TRPV5:CaM binding by implementing single molecule photobleaching counting, a technique with great potential for studying TRP channel regulation. In conclusion, our study proposes a new model for CaM- dependent regulation - calmodulation - of the Ca2+-selective TRPV5 that involves apoCaM interaction and lobe-specific actions.

cell biology↗

bioRxiv2021

Catestatin regulates the colonic mucus layer in inflammatory bowel disease

BackgroundThe pro-hormone chromogranin A (CgA) and its bioactive cleavage product catestatin (CST) are both associated with inflammatory bowel disease (IBD) and dysregulated barrier functions, but their exact role has remained elusive. Here, we demonstrate that CST regulates the colonic mucus layer. MethodsCST levels were measured in feces of IBD patients. The mucus layer, goblet cells, and immune cell infiltration were analyzed by histology and electron microscopy in colon tissue from IBD patients and mice with selective deletion of the CST-coding region of the CgA gene. ResultsCST levels were elevated in feces of IBD patients compared to healthy controls. The thickness of the mucus layer was increased in non-affected, but not in inflamed, regions of the colon in IBD patients. The thickness of the mucus layer and concomitant mucus production were also increased in the CST-KO mouse. This mucus phenotype in CST-KO mice could be reversed by bone marrow transplantation from wildtype mice. ConclusionsCST produced by bone-marrow derived immune cells reduces production of the mucus layer in the intestine. This might contribute to the reduced mucus layer in inflamed colon regions of IBD patients. Additionally, CST feces levels might be a biomarker for IBD.

immunology↗

bioRxiv2020

Glycocalyx-mediated Cell Adhesion and Migration

Cell migration is a force-dependent adaptive process mediated by integrin-dependent adhesion as well as other yet poorly defined interactions to the extracellular matrix. Using enzymatic multi-targeted digestion of sugar moieties on the surface of mesenchymal cells and leukocytes after interference with integrin function, we demonstrate that the surface glycocalyx represents an independent adhesion system. The glycocalyx mediates cell attachment to ECM ligand in the 100-500 pN force range and amoeboid migration in 3D environments in vitro and in vivo. Glycan-based adhesions consist of actin-rich membrane deformations and appositions associated with bleb-like and other protrusions forming complex-shaped sub-micron contact sites to ECM fibrils. These data implicate the glycocalyx in mediating generic stickiness to support nanoscale interactions (nanogrips) between the cell surface and ECM, mechano-coupling, and migration.

cell biology↗

bioRxiv2019

Modular actin nano-architecture enables podosome protrusion and mechanosensing

Basement membrane transmigration during embryonal development, tissue homeostasis and tumor invasion relies on invadosomes, a collective term for invadopodia and podosomes. An adequate structural framework for this process is still missing. Here, we reveal the modular actin nano-architecture that enables podosome protrusion and mechanosensing. The podosome protrusive core contains a central branched actin module encased by a linear actin module, each harboring specific actin interactors and actin isoforms. From the core, two actin modules radiate: ventral filaments bound by vinculin and connected to the plasma membrane and dorsal interpodosomal filaments crosslinked by myosin IIA. On stiff substrates, the actin modules mediate long-range substrate exploration, associated with degradative behavior. On compliant substrates, the vinculin-bound ventral actin filaments shorten, resulting in short-range connectivity and a focally protrusive, non-degradative state. Our findings redefine podosome nanoscale architecture and reveal a paradigm for how actin modularity drives invadosome mechanosensing in cells that breach tissue boundaries.

cell biology↗